The present invention relates to a method for the control of the chain drive mechanisms of underground working machines, especially chain scraper conveyors, as well as a corresponding chain scraper conveyor.
DE 43 16 798 A1, to whose published content reference is made here, proposes a generic underground chain drive mechanism, which is provided with a multiple disc clutch with hydraulic closing pressure adjustment and a measuring and control device, in order to satisfy the different requirements on modern drive systems with continuously rising installed performance, high reliability and high endurance of all components with a compact construction of the drive system. The drive mechanism for the chain operation of the underground working machine, especially of a face conveyor, comprises two drives, of which one forms the main drive and the other an auxiliary drive and each has a mains fed electrical drive motor, whose drive revolutions and motor torque which can be transmitted to a chain wheel via a two stage gearbox unit, of which at least the second is constructed as a planet drive. The core of each drive unit is a multiple disc clutch, which is assigned to the hollow wheel of the planet drive and detects and adjusts to the various operating conditions and functions, such as smooth starting, overload protection, load equalisation, creeping travel and high starting torque can be controlled. The multiple disc clutch comprises here a fixed clutch packet and a movable clutch packet joined to the hollow wheel, which are pressed together with the coupling pressure prescribed by the control, by means of a hydraulic cylinder controlled by a servo valve. By using a controlled retardation of the hollow wheel, its revolutions and, thereby, the slippage can be adjusted to any desired value between 0 and the maximum revolutions of the hollow wheel. For the control and the regulation of the drive, its operating data are continuously captured, the measured values are evaluated in the evaluation device and regulating values are output from a regulating circuit to the controller of the closing pressure adjustment. The multiple disc clutch is a wet running multiple disc coupling with special clutch linings, so that the power transmission is practically wear-free. The heat arising from slippage between the clutch packets is removed via heat exchangers and a cooling water circuit. The chain wheels of the main drive unit and the auxiliary drive unit drive the circulating chain together, which in face conveyors comprises horizontal and vertical chain elements as well as the scrapers.
In face conveyors with comparatively short chain lengths, i.e. a distance of up to some 350 m, the measuring and evaluation unit, together with the load equalisation, slippage control and overload protection, assures secure operation of the chain scraper conveyor, mostly without failures. With increasing chain lengths, especially in chain scraper conveyors with long chains, i.e. a distance between main and auxiliary drive units of more than 400 m, the problem of chain breakage in the bottom strand, i.e. the empty run of the chain, increases disproportionately. The applicant for the present application has conducted intensive research, to determine the cause of these chain breaks, so that constructional and/or control engineering measures to avoid chain breakages can be undertaken. The latest results from experimental measurements have shown that a chain break in the bottom run often precedes an upwards turning curve of the chain force, so that the cause of the chain break could lie in vibration phenomena of the chain. In this it was shown relatively quickly that transverse vibrations of the chain cold be eliminated as the cause of high dynamic chain forces, so that the investigations were broadened into longitudinal power swings.
Chain breakage in the bottom run presents a real problem, so that it is a main aim of the invention to ameliorate this problem. An attachment to avoid longitudinal swings in the chain by mechanical means, which increase the damping in the chain system, had to be abandoned because of too great a liability to wear, high cost and the greater need for maintenance within the permanently changing chain loading. The applicant of the present application has therefore gone over to reproduce a chain scraper conveyor, together with its drive arrangements and the chain in a model and to research in the model the causes for the vibration phenomena and to simulate measures for their removal.
The main result from this model building and simulation is that vibration phenomena, which finally lead to overloading such as chain breakage or to a shaft break, can be traced back to characteristic chain vibration effects. The chain vibrations depend here strongly on the friction of the chain in the top run and in the bottom run, including the specific characteristics of the friction curve. In the top run a damping is effected by the loading of the pans between the scrapers, which works against the occurrence of characteristic vibrations. In the bottom run on the other hand a substantially greater dependency of the characteristic vibrations on the friction curve is evident, since the characteristic curve of the friction of the chain has a negative gradient and the coefficient of friction reduces with increasing running speed of the chain.
Accordingly taking account of the results discussed above the invention is directed to a method for the control of vibration phenomena in chain driven underground working machines such as conveyor installations or mining extraction machines in which by means of a detection device a detection signal, representative of the current vibration arising in the chain, is filtered out from the operating data of the main and auxiliary drives and taken to an active suppressor, which in dependency on the detection signal, generates a time-variable signal in accordance with a suppression function, with which, in the frequency range of the vibration of the chain, a change is effected in the control value for the closing pressure setting of the multiple disc clutch of at least one, preferably both drive units by the abstraction of energy or the introduction of energy in the chain. For the first time a method is proposed with the present invention, in which information on the current state of vibration in the chain is obtained by means of a detection device and from this using an active suppressor a control signal is generated as a phase shifted exciter, which changes in the same frequency range as the vibration of the chain and by superimposition on the vibration leads to its damping or suppression. The method according to the invention can cost effectively be connected into the presently available regulating structure, integrated in the measuring and control device, since by means of the control signal a change is effected in one of the controlling values in the control structure. Chain drive arrangements with multiple disc clutches with closing pressure adjustment offer here the special advantage that a direct access to the process is possible by their construction and control structure. In drive units with multiple disc clutches it is actually possible to obtain a rapid change in the revolutions of the chain wheel by suitable reduction of the oil pressure in the closing pressure adjuster of the multiple disc clutch. By changing the closing pressure the slippage between the plates is caused to increase, and consequently the hollow wheel accelerates and the drive revolutions of the drive and the chain wheel are reduced. Conversely by increasing the closing pressure the hollow wheel can again be retarded and the chain wheel accelerated. These changes of the control value for the closing pressure setting can be carried out within the frequency range, which is necessary for the active suppression of the vibration. The preferred area of use of the method according to the invention is the suppression of the natural vibrations of the chain; since the method can be used for all the vibration phenomena within the chain driven working machine, the description covers the general case of vibrations.
Various possibilities offer themselves for the adaptation of the method, some preferred examples of which are indicated below. Thus the detection signal can be filtered out electronically from deviations of the measured motor current, motor revolutions, motor torque, drive revolutions, chain force, tensioning cylinder force or closing pressure adjustment using suitable filters and filter structures. It is understood that the sampling rate for filtering out the detection signal must be suitably high and for the calculation of the suppression function and generation of the control signal only short timing cycles are available.
In a preferred embodiment of the method a pulse-like pressure modulation of the closing pressure adjustment is effected by changing the control value in dependency on the control signal. It has been shown that with the pulse like changing of the closing pressure adjustment a rapid and deep acting intervention into the vibration condition of the chain drive can be achieved. In order to suppress the vibration it is then decisive that the first pressure change for introducing energy into the chain or abstracting energy from the chain starts with the correct phase shift related to the vibration and to tune its frequency or periodic duration sharply, so as to achieve an optimum suppression. To achieve this, each pulse cycle of the control signal for pressure modulation of the closing pressure adjustment can comprise at least one starting pulse and one ending pulse with reversed prefixes, whereby the starting pulse has a greater pulse width and lower amplitude than the ending pulse to achieve the abstraction or introduction of energy. The multiple disc clutch can then be adjusted more rapidly to the original control value by the higher and shorter ending pulse. With the pressure modulation a change in the revolutions and/or torque is consequently instigated on one or on both chain wheels, whereby the curve against time of the change is in a tuned ratio to the vibration, phase shifted to it and overlays the vibration, so that from this superimposition suppression of the vibration results. The tuned ratio between the vibration and the opposing vibration generated by pressure modulation can preferably lie at 1, i.e. the opposing vibration has the same frequency as the vibration, or correspond to a whole number multiple, i.e. the suppressing vibration is active only on every n-th. vibration of the chain.
The method can be especially advantageously implemented, if the measuring and evaluation device for each drive unit has a cascade regulation with a pressure control circuit to regulate the closing pressure and a slippage control circuit to regulate the slippage and superimposed on it for both drive units a common power regulator to equalise the load, as is the case with the drive units applied by the applicant (CST-drives). In this the control signal output from the suppressor can then be switched to the output signal or the output signals of the power regulator, so as to tie in the change of the control value or pressure modulation with the desired time relationship in the system. Only with the modified control structure is it possible to detect the vibration in the system, since in the old control circuit structures only the differences between two values are converted, as for instance with the regulator, or the ratios between two values as in the power equalising regulator, as adjusting interventions for the closing pressure adjustment. In the method according to the invention, on the other hand, the detection signal is preferably filtered out from the motor current or the drive revolutions, whilst the slippage is controlled in a pulse-like manner as the control value.
The method according to the invention has at the same time a wider area of application and can also be applied in those underground, chain driven working machines, which have an electric drive motor whose revolutions and torque can be transmitted by a gearbox unit to a chain wheel, and a measuring and regulating device for control, revolutions monitoring, overload protection, load equalisation and the capture of operating data from the main and auxiliary drives, whilst here also a detection signal, representing the current vibration arising is filtered out from the operating data of the main and auxiliary drives by means of a detection device and taken to an active suppressor, which, depending on the detection signal generates a time variable control signal in accordance with a suppressor function, with which a change in the conditions of at least one, preferably both drive units, in the frequency range of the vibration of the chain, is effected for the suppression of vibration by the abstraction of energy from, or the introduction of energy into the chain. The method can consequently also be applied with chain drive mechanisms, which do not have multiple disc clutches, but have electric drive motors in which the revolutions can be changed at will between minimum and maximum without steps. Such drive motors can especially be a drive assembly with frequency converter device, transformer and switching unit, so that the control signal of the suppressor passes via the switching unit to change the revolutions of the chain wheel or the chain wheels.
As set out at the beginning the invention also relates to chain scraper conveyors with the generic construction, which are in which the measuring and control device has a detection device, with which a detection signal representing the currently arising vibration in the chain can be filtered out from the operating data of the main and auxiliary drives, and has an active suppressor to which the detection signal can be taken, which depending on this generates a time-variable control signal in accordance with a suppression function, with which, in the frequency range of the vibration of the chain, a change can be effected to the control values for the closing pressure adjuster of the multiple disc clutch of at least one drive unit for the suppression of vibration in the chain by abstraction of energy or introduction of energy in the chain. As already set out the chain scraper conveyor has preferably a measuring and evaluating device with pressure and slippage control circuits and a power regulator, whereby the control signal output from the suppressor to change the control values is switched to the output signal or the output signals of the power regulator. In scraper chain conveyors it is especially favourable if the multiple disc clutch is wet running and preferably with oil flowing through it and the control value is the slippage, whereby the detection signal from the variations of the drive revolutions or the variations of the motor current is filtered out.